Forged 273 crank in an early 360 Block?

The compression numbers you have are based on published blueprint specs. Actual OEM deck heights and chamber volumes are usually more so that would lower compression a bit.

Using Magnum heads, you could also use Magnum style pistons to get the compression down. Just another option you would have to do the math on after measuring everything. Reducing quench can promote detonation in some cases even if compression is reduced. Quench promotes turbulence which helps combustion efficiency.

I don't know it going to bigger valves will result in much chamber volume difference. But I just don't understand giving up cubic inces. An efficient way to make more horsepower per cubic inch is to destroke, which racers do in Competition Eliminator classes that have a weight-to-cubic inch rule. At 10lbs per cubic inch, a 280 cubic inch engine in a 2,800lb car will be faster that a 300 cubic inch engine in a 3,000lb car if both engines are built with the same expertise. But when there are no rules or limits, more cubic inches will be faster at the same weight, with very few exceptions.